1. Field of the Invention
The present invention relates to methods and devices for electro-optically detecting the distance to an object and more particularly to active detecting devices and methods wherein a radiation beam is transmitted to the object and reflected back to photoelectric sensor means.
2. Description of Prior Art
Distance detecting devices are employed in a variety of prior art apparatus. For example such devices are useful in focus control systems, e.g. as rangefinders in cameras, to determine the proper focus position for a lens. There are many other uses for distance detection devices, and there are many different prior art structures and techniques for effecting such detection.
Active electro-optical distance detection devices, which form one useful class within a wide variety of distance detecting approaches, typically employ a light emitter(s), optical means (e.g. a lens) for directing emitted light toward the object to be sensed, a photoelectric detector(s) for sensing light reflected from the object and optical means for directing the reflected light onto the detector(s). U.S. Pat. Nos. 3,443,502; 3,720,148 and 4,065,778 are exemplary of triangulation techniques for active distance detection; the emitter means and detector means are spaced a known distance along a triangle base and the devices compute the object distance based on a measure of the angle between the emitted beam axis and the axis of the beam reflected from the object. These devices require separate projecting and receiving optics and precise relative positioning of the emitter and detector means.
The device disclosed in U.S. Pat. No. 3,617,128 differs from triangulation-type distance detectors in that light is directed to the object and reflected back to the detectors along a generally common axis. The object distance is determined as being within one of a plurality of discrete range-zones based on the size of the object's reflected light "blur circle" (i.e., the out of focus light spot formed at a detection plane, substantially normal to the optical axis of the device's receiving lens, by the object-reflected light). Blur circle size is determined only approximately as extending onto (or not extending onto) different ones of a plurality of detectors located at different positions in the detection plane. This device also uses separate projecting and receiving optics and requires accurate alignment of the lenses, the emitter and detectors.